The unusual carbon cycle budget of the Gravona (Corsica) - A small stream in a mountain silicate terrain

The current research of carbon cycling in inland waters lacks a sound knowledge of carbon outgassing from small streams. Consequently, the terrestrial water cycle compartments might still be seriously underrepresented in estimates of global carbon transfer budgets from land surfaces. This study investigated carbon sources and sinks of the high-relief silicate catchment of the Gravona river (Corsica, France) on the basis of field parameters, dissolved inorganic carbon (DIC) and its stable carbon isotopes (δ¹³C_DIC). The source region was characterised by low DIC and high δ¹³C_DIC. Higher respiration and weathering influences in the lower river sections induced increasing DIC concentrations and seasonality, while the δ¹³C_DIC decreased. The aqueous partial pressure (pCO_2(aq)) was lowest at the source. Samples from the cold season even showed undersaturation that led to atmospheric CO₂ uptake. Downstream, the seasonality of pCO_2(aq) increased with pronounced CO₂ degassing at the river mouth. Average DIC flux along the river was 0.129 Gg C yr^–1 and was almost equal to CO₂ degassing from the river surface with 0.128 Gg C yr^–1. Our study showed that on an annual basis the river is an overall weak to medium source of CO₂ to the atmosphere even though headwater parts of the river seasonally act as CO₂ sinks.